The present invention relates to an open-end ratchet wrench and, more particularly, to a wrench for adjusting screw jacks associated with conventional scaffolding. The wrench is adapted to simultaneously engage one leg or vertical frame member of the scaffold structure and an arm member extending laterally from the screw jack thereby facilitating rapid and effortless adjustment or levelling of individual scaffolding legs.
The use of scaffolding comprising tubular metal frame legs interconnected by a plurality of cross-braces is well known within the building construction and maintenance trades. For example, scaffolding is commonly used to support troughs during the pouring of concrete. Scaffolding structures, assembled either from individual members or from pre-assembled sections, may extend in excess of one-hundred feet both laterally as well as vertically. In order to compensate for ground or building surface irregularities to establish the proper grade for concrete pouring, or to lower the scaffolding for removal, screw jacks are positioned as required throughout the scaffolding structure.
The present invention is particularly intended for use with lead-screw type jacks having an internally threaded collar and bearing member with integral opposed arm members. Rotation of the collar forces the lead-screw to advance or retract as appropriate. Heretofore, adjustment of such screw jacks has generally been accomplished by manually rotating the arm members in a circular path or, where extreme compressive loads are encountered, a pipe positioned axially over an arm member may be required to apply sufficient force to reposition the jack. Such adjustment methods have generally been found to require excessive time and are therefore considered unsatisfactory.
The ratchet wrench of the instant invention, however, is adapted for substantially instantaneous engagement with the screw jack and for rapid rotation of the jack collar without time consuming repositioning of the wrench following each stroke. More particularly, the present wrench incorporates an asymmetrical head geometry adapted to receive the leg or frame member of a scaffold therein and to retain such frame member in locking engagement during the forward or screw advancing stroke. No time consuming wrench adjustments are required.
Automatic engagement of the jack collar arm members is achieved by a plurality of flippers or dog-members spaced around the wrench head and retained for pivotal movement thereon. In particular, these flippers are oriented perpendicularly to the wrench head and are generally vertical during normal wrench use. In this manner, gravity acts to automatically pivot the flippers into operative engagement with the jack arms during the forward stroke while permitting the flippers to rotate harmlessly out of engagement during the return or backward wrench stroke. Thus, the instant wrench is adapted to effortlessly engage a scaffolding screw jack and to quickly raise or lower the jack by a succession of reciprocal strokes.
Wrenches specially designed to operate screw jacks are known to the art. Unlike many conventional general purpose wrenches, however, screw jack wrenches are typically designed to mate and function with a particular or limited variety of jacks. The instant wrench, for instance, is specially suited for use with scaffolding or similar screw jacks having a collar and collar arm members adapted for rotation on a lead-screw. Thus, wrenches adapted for use with other jacks simply do not function in the instant environment.
Another example of a specialized jack is shown in Lewis, U.S. Pat. No. 740,878, wherein a ratchet type screw jack wrench is disclosed having a single spring-loaded dog-member retained for pivotal movement between, and parallel to, spaced head members. The dog is specially adapted to engage annular ratchet teeth rigidly secured to the jack screw. It will be appreciated that the Lewis '878 jack wrench is necessarily limited for use with jacks specially equipped with annular ratchet teeth.
Other special purpose wrenches known to applicant but unsuited for scaffolding screw jacks include Thompson, U.S. Pat. No. 2,659,257; Humburg, U.S. Pat. No. 1,964,121; Allmon, U.S. Pat. No. 1,291,633; and Moore, U.S. Pat. No. 2,539,262. Thompson '257 shows a turnbuckle ratchet wrench utilizing a plurality of spring-loaded pawl members retained, as in Lewis '878, for pivotal movement between, and parallel to, spaced head members. The specialized teachings of Thompson '257 are limited and find no application to scaffolding screw jacks as shown herein.
The asymmetrical head of the spanner wrench disclosed in Humburg '121, while potentially adaptable for use with scaffolding screw jacks, does not contemplate the positioning or `nesting` of a scaffolding leg within the opening provided in the head nor, importantly, does Humburg teach the instant arrangement whereby the particular head geometry was found to facilitate ratchet wrench operation. The other references are cited only to illustrate special purpose wrench structures but are not otherwise considered pertinent.
It is therefore an object of the present invention to provide a wrench specially adapted for use with scaffolding or similar screw jacks characterized by a rotatable element having an arm member to facilitate the rotation thereof. The wrench shall be easily positioned about the scaffolding leg or similar tubular member without need for wrench readjustment. Further, the wrench shall automatically engage the arm members of the jack for rotation in a first direction and automatically disengage the arm members in the second or return direction thereby facilitating the ratchet type operation of the wrench. The wrench shall be adapted to permit either the raising or lowering of the screw jack simply and automatically by properly positioning the wrench with respect to the jack.